1. Field of the Invention
The present invention relates generally to powder dispensers and more particularly to the pulmonary route of drug administration.
2. Description of the Prior Art
The lungs present an attractive alternative to parenteral and oral routes for the administration of drugs for the treatment of systemic as well as pulmonary disorders. This is due to the large surface area and extensive vascularization of the lung, as well as to the high permeability of the airway and alveolar epithelia.
Much of the current interest in the pulmonary route of drug delivery has centered on the development of methods which use jet nebulizers or MDI's (multiple dose inhalers) for the administration of aerosols of solutions of a variety of drug substances such as antibiotics, bronchodilators, anti-inflammatory steroids, antiproteases, polypeptides, surfactant and gene transfer products. However, while this approach offers relative freedom from a number of systemic side-effects when compared with parenteral or oral methods, the efficiency of delivery is typically low (1-20%), and there are undesirable local side-effects such as cough, airway irritation and bronchoconstriction. Furthermore, substances which are not water-soluble are generally not amenable to this approach. Finally, the chlorofluorocarbons which are typically used as propeilants in MDI's are currently being phased out for environmental reasons.
For these reasons, attention has recently shifted to the possibility of using inhaled dry powders as a way of accessing the pulmonary route of drug administration. These studies almost invariably involve a device in which a small, precisely-metered amount of powder is presented to an airstream generated by the patient's inhalation, although additional sources of energy (mechanical disruption, compressed air) are occasionally used to improve powder dispersion. Due to the inherent variability in a number of factors, including oropharyngeal geometry, force of inhalation, powder formulation, and the fraction of the powder "dose" actually presented to the airstream in the device, the delivery of a precise amount of a dry powder to the lower respiratory tract by inhalation is highly problematic. For example, in human trials of prior art dry powder inhalers, only 5-14% of the available powder dose actually reached the lungs. Furthermore, while these types of inhalers may be appropriate for prophylactic administration of drugs such as insulin or parathyroid hormone, patients with asthma or other forms of acute bronchoconstriction are unable to generate enough airflow to activate these devices. This is especially true of children and infants.
In view of the foregoing, it is apparent that there is a strong need for both improved pulmonary delivery for drug administration and also in dispensers which can be adapted for this purpose.